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Ideassimples
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- TL;DR Summary
- The cosmic microwave background questions the relativity of simultaneity.
(I hope my English is understood). Hello, I have a question regarding the relativity of simultaneity.
The mean temperature of the cosmic microwave background tells us how big the universe is with respect to the recombination epoch. If I now measure that the mean temperature of the cosmic microwave background is 3 Kelvin, and I know that at the time of recombination it was 3000 Kelvin, then I can deduce that the universe is now (3000/3 = 1000) 1000 times more larger than in the recombination era. From then until now the universe has been expanding to multiply by 1000 its size.
The mean temperature of the cosmic microwave background is the same for two observers who measure it simultaneously, regardless of their relative motion. Two observers with relative movement between them, by Doppler effect, may not agree on the temperature of the cosmic microwave background in a certain direction, but if they both make the measurements simultaneously, they will both measure the same mean temperature of the cosmic microwave background.
And this is problematic. Let me explain, let's imagine two radio telescopes with no relative motion between them, radio telescope 1 and radio telescope 2. Both radio telescopes can measure the mean temperature of the cosmic microwave background with great precision. Radio telescopes are turned on by hitting their switch with a beam of light.
Right in the center is a light source, with no relative motion relative to radio telescopes. The light source sends a beam of light to each radio telescope, hits the switch, turns them on. Both radio telescopes measure the mean temperature of the cosmic microwave background. It turns out that both radio telescopes get exactly the same result.
Observer A is not moving relative to the system. From the reference frame of observer A, the light rays reach both radio telescopes at the same time. Therefore observer A sees that both radio telescopes are turned on at the same time. Observer A is told that both radio telescopes measured exactly the same mean temperature of the cosmic microwave background. Since observer A saw that both radio telescopes measured the mean temperature of the cosmic microwave background at the same time, he understands that the data agrees with his observation.
Observer B does move relative to the system. From the reference frame of observer B, first a ray of light arrives at radio telescope 1, and then a ray of light arrives at radio telescope 2. Therefore observer B sees that radio telescope 1 turns on first and radio telescope 2 later. Observer B is told that both radio telescopes measured exactly the same mean temperature of the cosmic microwave background. Observer B understands that there is a conflict between his observations and the measurements from the radio telescopes.
Since from the reference frame of observer B, radio telescope 1 is turned on first and then radio telescope 2, observer B expects that the measurement of the mean temperature of the cosmic microwave background of radio telescope 1 is higher than that of radio telescope 2. Without However this does not happen, both measures are identical.
Then observer B reaches the following conclusion:
-Or for a certain period of time, from its reference frame, the universe stopped expanding.
-Or the simultaneity is not relative, but absolute.
What do you think?
The mean temperature of the cosmic microwave background tells us how big the universe is with respect to the recombination epoch. If I now measure that the mean temperature of the cosmic microwave background is 3 Kelvin, and I know that at the time of recombination it was 3000 Kelvin, then I can deduce that the universe is now (3000/3 = 1000) 1000 times more larger than in the recombination era. From then until now the universe has been expanding to multiply by 1000 its size.
The mean temperature of the cosmic microwave background is the same for two observers who measure it simultaneously, regardless of their relative motion. Two observers with relative movement between them, by Doppler effect, may not agree on the temperature of the cosmic microwave background in a certain direction, but if they both make the measurements simultaneously, they will both measure the same mean temperature of the cosmic microwave background.
And this is problematic. Let me explain, let's imagine two radio telescopes with no relative motion between them, radio telescope 1 and radio telescope 2. Both radio telescopes can measure the mean temperature of the cosmic microwave background with great precision. Radio telescopes are turned on by hitting their switch with a beam of light.
Right in the center is a light source, with no relative motion relative to radio telescopes. The light source sends a beam of light to each radio telescope, hits the switch, turns them on. Both radio telescopes measure the mean temperature of the cosmic microwave background. It turns out that both radio telescopes get exactly the same result.
Observer A is not moving relative to the system. From the reference frame of observer A, the light rays reach both radio telescopes at the same time. Therefore observer A sees that both radio telescopes are turned on at the same time. Observer A is told that both radio telescopes measured exactly the same mean temperature of the cosmic microwave background. Since observer A saw that both radio telescopes measured the mean temperature of the cosmic microwave background at the same time, he understands that the data agrees with his observation.
Observer B does move relative to the system. From the reference frame of observer B, first a ray of light arrives at radio telescope 1, and then a ray of light arrives at radio telescope 2. Therefore observer B sees that radio telescope 1 turns on first and radio telescope 2 later. Observer B is told that both radio telescopes measured exactly the same mean temperature of the cosmic microwave background. Observer B understands that there is a conflict between his observations and the measurements from the radio telescopes.
Since from the reference frame of observer B, radio telescope 1 is turned on first and then radio telescope 2, observer B expects that the measurement of the mean temperature of the cosmic microwave background of radio telescope 1 is higher than that of radio telescope 2. Without However this does not happen, both measures are identical.
Then observer B reaches the following conclusion:
-Or for a certain period of time, from its reference frame, the universe stopped expanding.
-Or the simultaneity is not relative, but absolute.
What do you think?